It’s less about density and urban layout, and more about culture and the way we make use of where we live.

Ride-sharing, including sharing taxis, has many advantages: you save money, you pollute less, you get to use the carpool lane, and you can check Facebook on your phone instead of having to drive the car. Despite these benefits, not all cities are equally suited to car-sharing. A new study from MIT examines cities around the world to figure out where ride-sharing would fare well–and where it would have a tougher time catching on.

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The study, from the Senseable City Lab at MIT, draws on a 2014 study from the same research group on New York City, which tracked the trips made by 13,000 New York City cabs over the period of a year. That study found that almost 95% of trips taken through New York could be shared. By deliberately doing so, drivers could reduce their total travel time by as much as 40%; operational costs and carbon emissions would also plummet accordingly. Even when trying to coordinate shared trips on the fly via smartphone apps, drivers could likely cut down their travel time by 32%. The results of that study were obvious: If everyone used ride-sharing instead of private cars or single-passenger taxis, the benefits would be huge. But for the follow-up study, the researchers wanted to know: Does this logic apply to every city, or can it only work in the super-dense Manhattan, where the original study took place?

The new study compares San Francisco, Singapore, and Vienna to New York. To find out how many rides were shareable, the researchers tracked 500 taxis in San Francisco, 16,000 in Singapore, and 1,000 in Vienna over the course of a month; for New York, they used data from the original 13,000 taxis. Factors contributing to ride-sharing feasibility included the size of the city, the average speed of the cars, and the waiting times that would be acceptable to passengers hitching a ride.

What the researchers found is that the three other cities were almost as well-suited to ride-sharing as New York. The new study estimates that over 99% of New York trips are shareable, while in San Francisco, Singapore, and Vienna, 97% are shareable. So close were these four cities in their suitability that the researchers were a come up with a set of guidelines that enabled them to predict which other cities would take well to ride-sharing. They drew up a list of 30 other cities, ranked in order of their ride-sharing potential: Amsterdam and Prague fell near the top; London and Berlin near the bottom (happily, both London and Berlin have excellent public transit options).

It’s notable (and surprising to the researchers) that density and layout were not the most important factors when it came down to determining ride-share feasibility. Of course, they had a slight effect: Sprawling cities like London and Berlin were deemed less suitable for sharing by the study, but the four key cities in the study all had drastically different layouts and similar suitability. “The possible explanation,” co-author Paolo Santi told MIT News, “is that what influences shareability is the way our lives are organized, rather than the city layout.”

So for instance, a less-dense city like Vienna makes a good candidate for ride-sharing because of the way its residents move throughout the city on a daily basis. That comes down to familiar factors of livability: the efficacy of other transit options and how far people have to travel for work, shopping, and entertainment.

And of course, there’s the matter of whether or not people are willing to share a trip wit a stranger. Without that, the whole car-sharing idea goes out the window. “How shareability turns into real sharing depends on culture,” co-author Carlo Ratti told MIT News. “In some countries, you might find more sharing than in other countries.”

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Previously found writing at Wired.com, Cult of Mac and Straight No filter.